This invention generally relates to systems and methods for sensing when an aircraft has entered a volcanic plume. As used herein, the term “volcanic plume” means a cloud of volcanic ash. In particular, this invention relates to systems and methods for onboard optical detection of volcanic ash suspended in the atmosphere through which an aircraft is flying.
Volcanic ash can pose a hazard to flying jet aircraft, threaten the health of people and livestock, damage electronics and machinery, and interrupt power generation and telecommunications. Volcanic ash comprises tiny jagged particles of rock and natural glass blasted into the air by a volcano. Wind can carry ash thousands of miles, affecting far greater areas than other volcano hazards.
Volcanic plumes present two problems for aircraft: (a) engine shutdown due to ash; and (b) aircraft damage and/or crew and passenger injury due to ash and corrosive gases. Volcanic ash particles are extremely abrasive. They are jagged particles of rock and glass that can cause rapid wear to the internal workings of jet engines. More important, high temperatures in some parts of jet engines can melt the ash; it then re-solidifies on cooler parts of the engine, forming a layer that blocks airflow, interferes with moving parts, and eventually shuts down the engine.
Another issue is the potentially harmful effects of elevated concentrations of SO2 and sulfate aerosol in ash-poor clouds on aircraft and avionics. In addition, volcanic ash particles, with sulfuric acid adhered thereto, are tiny enough to travel deep into the lungs of human beings, which may be harmful and potentially fatal to people.
The overall technical problem is to provide means for detecting airborne volcanic ash at cruise altitude and then alerting aircraft so they can avoid damage or injury from passage through the volcanic plume. The specific technical problem is to detect volcanic ash in the immediate vicinity of an aircraft at concentrations high enough to damage the airplane or personnel, but too low to be seen by the naked eye.
Three general approaches to solving the specific technical problem of detecting the presence of volcanic ash particles in the atmosphere surrounding an aircraft are the following: (1) naked eye observation; (2) forecasts of locations where volcanic ash may be encountered at various times, based on satellite measurements, pilot reports and a variety of other measurements, all integrated into weather models; and (3) active optical sensors attached to the aircraft and configured to make optical measurements of scattering or attenuation of light from an onboard source (e.g., laser pulses) by the atmosphere outside the aircraft. Each of these approaches has shortcomings.
(1) Naked eye observation is almost entirely dependent on the flight crew, not the cabin crew or passengers. The flight crew typically looks forward from the cockpit, not sideways and backward to the air near the wingtip strobes. Therefore, naked eye observation relies on ambient light. Also naked eye observation has the sensitivity of a human eye which is limited, especially for senior crew members. Also, human vision is insensitive to slow changes in intensity, as when an aircraft enters a plume whose edge is marked by slowly increasing ash density. Lastly, human crew members typically have many duties so they cannot monitor scattering full-time.
(2) Volcanic plume forecasts provide coarse spatial resolution over large regions and are based on non-real-time data.
(3) Prior art with active optical scattering requires installation of a special-purpose optical emitter. For example, the German Aerospace Center completed a successful measurement flight of the volcanic plume over Germany on Apr. 19, 2010. The scientific instruments onboard the research aircraft were installed in the cabin and underneath the wings. A LIDAR (Light Detection and Ranging) instrument was installed in the cabin. Measurements were made via air inlets and optical windows in the roof and the floor of the research aircraft. The LIDAR instrument transmitted laser impulses and received the backscatter signal from the atmosphere.
The problem of detecting the presence of volcanic ash particles in the atmosphere surrounding an aircraft is especially acute at night. In daylight, a diffuse plume of ash spread over several miles may scatter enough light to be visible during an edge-on approach to the plume: the integrated intensity of light scattered by miles of ash is enough to be seen by the naked eye. At night, however, the only illumination of a volcanic plume may come from lights on the airplane. For example, to reduce the risk of in-flight collisions between aircraft, aircraft are required to be equipped with strobe warning lights (e.g., on the wing tips and tail), which pulse a high-intensity, short-duration white light approximately once per second. Alternatively, most modem aircraft are equipped with landing lights which are used to illuminate the terrain and runway ahead during takeoff and landing. Although landing lights are usually extinguished in cruise flight, the landing lights could be turned on in cruise flight (except on those aircraft whose landing lights can only be turned on when the landing gear are extended).
The intensity of illumination from an external light source falls rapidly with distance from the airplane. Therefore, there may not be enough integrated backscatter for human crews to visually detect the volcanic plume until it is so dense that the airplane is damaged.
There exists a need for an easily installed system that will detect the presence of volcanic ash in the surrounding atmosphere using existing light sources on an aircraft, such as a strobe warning light or a forward-facing landing light.